/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.sdk.metrics;



import com.bff.gaia.unified.sdk.annotations.Experimental;

import com.bff.gaia.unified.sdk.annotations.Experimental.Kind;



import java.io.Serializable;



/**

 * The <code>Metrics</code> is a utility class for producing various kinds of metrics for reporting

 * properties of an executing pipeline.

 *

 * <p>Metrics are created by calling one of the static methods in this class. Each metric is

 * associated with a namespace and a name. The namespace allows grouping related metrics together

 * based on the definition while also disambiguating common names based on where they are defined.

 *

 * <p>Reported metrics are implicitly scoped to the transform within the pipeline that reported

 * them. This allows reporting the same metric name in multiple places and identifying the value

 * each transform reported, as well as aggregating the metric across

 *

 * <p>It is runner-dependent whether Metrics are accessible during pipeline execution or only after

 * jobs have completed.

 *

 * <p>Example:

 *

 * <pre><code> class SomeDoFn extends{@literal DoFn<String, String>} {

 *   private Counter counter = Metrics.counter(SomeDoFn.class, "my-counter");

 *

 *  {@literal @}ProcessElement

 *   public void processElement(ProcessContext c) {

 *     counter.inc();

 *     Metrics.counter(SomeDoFn.class, "my-counter2").inc();

 *   }

 * }</code></pre>

 *

 * <p>See {@link MetricResults} (available from the {@code PipelineResults} interface) for an

 * example off how to query metrics.

 */

@Experimental(Kind.METRICS)

public class Metrics {



  private Metrics() {}



  /**

   * Create a metric that can be incremented and decremented, and is aggregated by taking the sum.

   */

  public static Counter counter(String namespace, String name) {

    return new DelegatingCounter(MetricName.named(namespace, name));

  }



  /**

   * Create a metric that can be incremented and decremented, and is aggregated by taking the sum.

   */

  public static Counter counter(Class<?> namespace, String name) {

    return new DelegatingCounter(MetricName.named(namespace, name));

  }



  /** Create a metric that records various statistics about the distribution of reported values. */

  public static Distribution distribution(String namespace, String name) {

    return new DelegatingDistribution(MetricName.named(namespace, name));

  }



  /** Create a metric that records various statistics about the distribution of reported values. */

  public static Distribution distribution(Class<?> namespace, String name) {

    return new DelegatingDistribution(MetricName.named(namespace, name));

  }



  /**

   * Create a metric that can have its new value set, and is aggregated by taking the last reported

   * value.

   */

  public static Gauge gauge(String namespace, String name) {

    return new DelegatingGauge(MetricName.named(namespace, name));

  }



  /**

   * Create a metric that can have its new value set, and is aggregated by taking the last reported

   * value.

   */

  public static Gauge gauge(Class<?> namespace, String name) {

    return new DelegatingGauge(MetricName.named(namespace, name));

  }



  /**

   * Implementation of {@link Distribution} that delegates to the instance for the current context.

   */

  private static class DelegatingDistribution implements Metric, Distribution, Serializable {

    private final MetricName name;



    private DelegatingDistribution(MetricName name) {

      this.name = name;

    }



    @Override

    public void update(long value) {

      MetricsContainer container = MetricsEnvironment.getCurrentContainer();

      if (container != null) {

        container.getDistribution(name).update(value);

      }

    }



    @Override

    public void update(long sum, long count, long min, long max) {

      MetricsContainer container = MetricsEnvironment.getCurrentContainer();

      if (container != null) {

        container.getDistribution(name).update(sum, count, min, max);

      }

    }



    @Override

    public MetricName getName() {

      return name;

    }

  }



  /** Implementation of {@link Gauge} that delegates to the instance for the current context. */

  private static class DelegatingGauge implements Metric, Gauge, Serializable {

    private final MetricName name;



    private DelegatingGauge(MetricName name) {

      this.name = name;

    }



    @Override

    public void set(long value) {

      MetricsContainer container = MetricsEnvironment.getCurrentContainer();

      if (container != null) {

        container.getGauge(name).set(value);

      }

    }



    @Override

    public MetricName getName() {

      return name;

    }

  }

}